The continued development, study, and bioanalytical applications of novel polyion and anion selective polymer membrane/film-based electrochemical and optical sensors are proposed. Research during the next phase of this long-term project will build upon several significant discoveries/advances made during the most recent project period relating to potentiometric polyion sensing and new chemistries for anion-selective sensors. These include dramatically lowering the detection limits toward biomedically important polyions (e.g., heparin, protamine, etc.) via use of a novel rotating potentiometric membrane electrode configuration, and 2) uncovering a unique hydroxide ion bridged dimer/monomer equilibrium that can exist for certain metalloporphyrins when used as ionophores in organic polymer films for devising anion sensing electrodes. Future efforts will include both fundamental and applied studies in both the polyion and anion sensing areas. Specific goals for the polyion sensor efforts include: a) better understanding the nature (size, stoichiometry, etc.) of the ion-exchanger/polyion complexes that form within the polymer membranes used to fabricate such devices; b) demonstrating broader bioanalytical applications of the new, more sensitive rotating polyion sensing membrane electrode configuration; c) investigating the use of polyion sensors (including rotating arrangement) to detect polycationic dendrimers and their interaction with DNA; and d) further development of a completely new and rapid homogeneous immunoassay method for detecting of small, clinically and environmentally important analytes using polyions as labels. In the area of anion sensors, efforts will focus on establishing which metalloporphyrins can spontaneously form hydroxide ion bridged dimer structures within polymeric films, and determining how these reactions affect the response properties of anion selective electrodes formulated with such ionophores. In addition, studies will be undertaken to utilize this novel chemistry to devise completely new polymer film-based optical sensors for anions and neutral species (amines, gases, etc.) based on the ability of such ligating species to break metalloporphyrins dimers into monomers within the organic films, yielding a large shift in the lambdamax of the Soret band. Investigations of electrochemical anion sensors based on a new type of lipophilic dendntic anion-exchanger structure are also proposed. It is anticipated that this research will continue to provide the analytical community with a wide array of new and/or improved chemical sensors as well as novel sensor-based methods that will have immediate applications as tools for basic research and within modem clinical and environmental test instrumentation.